Relaxed silicon germanium (SiGe) on strain relaxed buffer (SRB) has been chosen as the up-front option for 7 nanometer (nm) complementary metal-oxide semiconductor (CMOS) technology. However, building CMOS on bulk SiGe substrate comes with new challenges.
One notable challenge is the formation of well doping. P-well doping with boron as dopant is not generally a problem (i.e., because boron diffuses even slower in SiGe than in silicon (Si)). However, forming an n-well presents some notable challenges. Arsenic is the typical choice for n-well doping under the p-channel field effect transistor (pFET) active regions. Arsenic has a much higher diffusion in SiGe than it does in silicon (Si), leading to unwanted diffusion of arsenic laterally into the p-well region and/or upward into the pFET channel region during thermal processing, destroying the devices. Phosphorus (another n-well dopant) diffuses slightly less, but the overall problem remains the same.
Shallow trench isolation (STI) currently is at a maximum of 100 nm. A 5×1017-1×1018 arsenic well implant goes deeper than that, especially with its increased diffusion value in SiGe.
Therefore, improved doping and isolation techniques are needed for relaxed SiGe on SRB technology.